Passing a string by reference and manipulate the string

Question

I am trying to pass a string by reference and manipulate the string in the function:

fn manipulate(s: &mut String) {                                                                                                                                                                                                          
  // do some string manipulation, like push
  s.push('3');  // error: type `&mut collections::string::String` 
                // does not implement any method in scope named `push`
}

fn main() {
  let mut s = "This is a testing string".to_string();
  manipulate(&s);          
  println!("{}", s);       
}

I have looked at examples on borrowing and mutibility. Also tried (*s).push('3'), but got

error: type `collections::string::String` does not implement any method in scope named `push`

I'm sure there's something obvious I'm missing or perhaps more reference material to read, but I'm not sure how to proceed. Thanks!

The change push_char -> push must be relatively recent, since I don't recall encountering it the last time I used that part of String functionality. What version are you using (if nightly, from what date)? — user395760
– user395760, Commented Oct 1, 2014 at 22:05
The version I am using is rustc 0.12.0-nightly (740905042 2014-09-29 23:52:21 +0000) — EricC
– EricC, Commented Oct 2, 2014 at 2:42
To correct the previous comment I made. I tried the same code on a different machine, which has rustc 0.12.0-nightly (740905042 2014-09-29 23:52:21 +0000). The error that result is actually a lot more informative: error: cannot borrow immutable dereference of &-pointer as mutable. Basically it is exactly as @IdolfHatler described! — EricC
– EricC, Commented Oct 2, 2014 at 2:49

IdolfHatler · Accepted Answer · 2014-10-02 00:15:21Z

15

Your code works with a slight modification on the newest version of rustc.

fn manipulate(s: &mut String) {                                                                                                                                                                                                          
  s.push('3');
}

fn main() {
  let mut s = "This is a testing string".to_string();
  manipulate(&mut s);          
  println!("{}", s);       
}

answered Oct 2, 2014 at 0:15

IdolfHatler

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